A galvanometer has resistance 54 Ω and gives full-scale deflection at 1 mA. It is to be converted into a 50 V voltmeter and a 10 mA ammeter. Which statements are correct?
A. voltmeter series resistance ≈ 50 kΩ,
B. ammeter shunt ≈ 0.2 Ω,
C. ammeter shunt ≈ 6 Ω,
D. voltmeter series resistance ≈ 5 kΩ,
E. voltmeter series resistance ≈ 500 Ω.

Question

A galvanometer has resistance 54 Ω and gives full-scale deflection at 1 mA. It is to be converted into a 50 V voltmeter and a 10 mA ammeter. Which statements are correct?

A. voltmeter series resistance ≈ 50 kΩ,

B. ammeter shunt ≈ 0.2 Ω,

C. ammeter shunt ≈ 6 Ω,

D. voltmeter series resistance ≈ 5 kΩ,

E. voltmeter series resistance ≈ 500 Ω.

G1 Physics · Accepted Answer

For the voltmeter: V = Iɢ(Rɢ + R) 50 = 0.001(54 + R) R = 49,946 Ω ≈ 50 kΩ So A is correct. For the ammeter: Total current = 10 mA Galvanometer current = 1 mA Shunt current = 9 mA Equal voltage across galvanometer and shunt: IɢRɢ = Iₛr (1 mA)(54 Ω) = (9 mA)r r = 6 Ω So C is correct. Hence A and C are correct: option D.